MRI compatible lead

ABSTRACT

A lead wire assembly apparatus for an implantable medical device (IMD), the apparatus including a lead having first and second ends and a plurality of separate conductive segments serially located therebetween; a cover defining at least one cavity situated about ends of adjacent conductive segments; and a fluid located in the at least one cavity and coupling the adjacent conductive segments to each other. The fluid electrically couples adjacent conductive segments to pass driving signals of the implantable medical device. The fluid may further attenuate induced signals generated by radiofrequency (RF) signals of a magnetic resonance (MR) system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/096,089 entitled, “MRI COMPATIBLE LEAD,” filed on Apr. 11, 2016,which is a continuation of U.S. patent application Ser. No. 14/924,524entitled, “MRI COMPATIBLE LEAD,” filed on Oct. 27, 2015, which is acontinuation of U.S. patent application Ser. No. 14/660,764 entitled,“MRI COMPATIBLE LEAD,” filed on Mar. 17, 2015, which is a continuationof U.S. patent application Ser. No. 14/481,710 entitled, “MRI COMPATIBLELEAD,” filed on Sep. 9, 2014, which claims the benefit of U.S. PatentApplication Ser. No. 61/875,492 entitled, “MRI COMPATIBLE LEAD,” filedon Sep. 9, 2013. The contents of all of the above-noted applications areincorporated herein by reference as if set forth in full and priority tothese applications is claimed to the full extent allowable under U.S.law and regulations.

FIELD OF THE PRESENT SYSTEM

The present system relates to an electrical lead which is compatiblewith use in magnetic resonance (MR) systems and, more particularly, toan electrical lead suitable for use in implanted devices which can becompatible for use within MR systems, and a method of operation thereof.

BACKGROUND OF THE PRESENT SYSTEM

Conventional implanted medical devices (IMDs) such as cardiacpacemakers, defibrillator or other neurostimulation devices (e.g., aphrenic nerve stimulators, deep brain stimulators, cochlear implants orvagal nerve stimulators) and the like are implanted within millions ofpatients. Unfortunately, these IMDs are incompatible for use withmagnetic resonance (MR) imaging (MRI) methods for many reasons includingthat conventional IMDs may interact with fields (e.g., static and/orpulsed) of MR systems. For example, MR systems during imaging utilizeradiofrequency (RF) emissions provided within a static magnetic fieldfor eliciting emissions from a region of interest (ROI) such as aportion of a patient's anatomy. These elicited emissions are received bythe MR system and are utilized for creating an image of the ROI by theMR system.

However, for a patient which has an IMD, the conductive portions such aslead wire of the IMD may act as an antenna to the RF emissions of the MRsystem which may result in RF heating of the lead wire due to inducedstanding waves within the lead wire. RF induced heating of the lead wiremay cause heating of nearby tissue resulting in general patientdiscomfort and/or burning of the tissue. Accordingly, patients in whichconventional IMDs are implanted cannot be safely scanned using MRmethods and are typically scanned using less desirable imaging methodssuch as computed tomography (CT), X-ray methods, and the like, whichemit ionizing radiation and may have inferior image resolutionparticularly of soft tissue present in the ROI.

Accordingly, embodiments of the present system may overcome these and/orother disadvantages of conventional systems and methods.

SUMMARY OF THE PRESENT SYSTEM

The system(s), device(s), method(s), arrangements(s), user interface(s),computer program(s), processes, etc. (hereinafter each of which will bereferred to as system, unless the context indicates otherwise),described herein may address problems in prior art systems.

In accordance with embodiments of the present system, there is discloseda lead wire assembly apparatus for an implantable medical device (IMD),the apparatus including a lead having first and second ends and aplurality of separate conductive segments serially located therebetween;a cover defining at least one cavity situated about ends of adjacentconductive segments; and a fluid located in the at least one cavity andcoupling the adjacent conductive segments to each other. The fluidelectrically couples adjacent conductive segments to pass drivingsignals of the implantable medical device. The fluid may furtherattenuate induced signals generated by radiofrequency (RF) signals of amagnetic resonance (MR) system. First and second ends of the lead maydefine a length of the lead wire which is greater than one-halfwavelength length of radiofrequency (RF) signals generated by an MRIsystem. A length of at least one of the plurality of conductive segmentsmay be less than one-half wavelength length of the radiofrequency (RF)signals generated by the MR system. The fluid may include a buffer, aconductive fluid or an ionic solution. In accordance with embodiments ofthe present system, the cavity is a first cavity and ends of adjacentconductive segments are located within the first cavity coupled tocorresponding conductive cylinders with a first conductive cylinder ofthe corresponding conductive cylinders sized to fit within a secondcavity formed by a second conductive cylinder of the correspondingconductive cylinders. The lead may be situated between and coupled to asignal generator and an interface probe.

In accordance with embodiments of the present system, an implantablemedical device is provided including a signal generator configured togenerate a driving signal; at least one controller configured to controlthe signal generator to generate the driving signal; a lead includingfirst and second ends and a plurality of separate conductive segmentsserially located therebetween with the first end coupled to the signalgenerator, a cover defining at least one cavity, and a fluid located inthe at least one cavity with the fluid electrically coupling adjacentconductive segments to each other; and an interface probe coupled to thesecond end of the lead. The fluid electrically couples adjacentconductive segments to pass the driving signal to the interface probe.The fluid may further attenuate induced signals generated byradiofrequency (RF) signals of a magnetic resonance (MR) system. Thefirst and second ends of the lead may define a length of the lead whichis greater than one-half wavelength length of radiofrequency (RF)signals generated by an MR system. A length of at least one of theplurality of conductive wire segments may be less than one-halfwavelength length of the radiofrequency (RF) signals generated by the MRsystem. The fluid may include a buffer, a conductive fluid or an ionicsolution. The cavity may be a first cavity and ends of adjacentconductive segments may be located within the first cavity coupled tocorresponding conductive cylinders with a first conductive cylinder ofthe corresponding conductive cylinders sized to fit within a secondcavity formed by a second conductive cylinder of the correspondingconductive cylinders.

In accordance with embodiments of the present system, a method offorming a lead for attenuating signals induced by radiofrequency (RF)signals of a magnetic resonance (MR) system, where the method includesacts of forming a lead having first and second ends and a plurality ofseparate conductive segments serially located therebetween; forming acover defining at least one cavity in which adjacent ends of conductivesegments are located; and electrically coupling adjacent conductivesegments to each other within the at least one cavity using a fluidcoupling.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is explained in further detail in the followingexemplary embodiments and with reference to the figures, where identicalor similar elements are partly indicated by the same or similarreference numerals, and the features of various exemplary embodimentsbeing combinable. In the drawings:

FIG. 1A shows a side view of a portion of a fluid-sealed connector (FSC)of an implantable medical device in accordance with embodiments of thepresent system;

FIG. 1B shows a side view of a portion of an FSC of an implantablemedical device in accordance with embodiments of the present system;

FIG. 1C shows a side view of a portion of an FSC of an implantablemedical device in accordance with embodiments of the present system;

FIG. 1D shows a side view of a portion of an FSC of an implantablemedical device in accordance with embodiments of the present system;

FIG. 2 shows an end view of a portion of the FSC of FIG. 1A inaccordance with embodiments of the present system;

FIG. 3 shows a cutaway view of a portion of the FSC taken along lines3-3 of FIG. 3 in accordance with embodiments of the present system;

FIG. 4 shows a cutaway exploded side view of a portion of an FSC inaccordance with embodiments of the present system;

FIG. 5 shows a cutaway view of a portion of the first cylinder of an FSCtaken along lines 5-5 of FIG. 4 in accordance with embodiments of thepresent system;

FIG. 6 shows a cutaway view of a portion of the second cylinder of theFSC taken along lines 6-6 of FIG. 4 in accordance with embodiments ofthe present system;

FIG. 7 shows an end view of a portion of the disc of FIG. 4 inaccordance with embodiments of the present system;

FIG. 8 shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system;

FIG. 9 shows a portion of a system in accordance with embodiments of thepresent system;

FIG. 10 which shows a block diagram illustrating an FSC operating inaccordance with embodiments of the present system within an MRI systemhaving an RF coil which may transmit RF signals;

FIG. 11A shows a block diagram of a portion of a lead having a pluralityof FSCs coupled together in series in accordance with embodiments of thepresent system;

FIG. 11B shows a block diagram of a portion of an implantable medicaldevice including the lead situated between and coupling a signalgenerator and an interface probe (IP) such as an implantable cardiacprobe in accordance with embodiments of the present system;

FIG. 12A shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system;

FIG. 12B shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system;

FIG. 12C shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system;

FIG. 12D shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system;

FIG. 12E shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system; and

FIG. 12F shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system.

DETAILED DESCRIPTION OF THE PRESENT SYSTEM

The following are descriptions of illustrative embodiments that whentaken in conjunction with the following drawings will demonstrate theabove noted features and advantages, as well as further ones. In thefollowing description, for purposes of explanation rather thanlimitation, illustrative details are set forth such as architecture,interfaces, techniques, element attributes, etc. However, it will beapparent to those of ordinary skill in the art that other embodimentsthat depart from these details would still be understood to be withinthe scope of the appended claims. Moreover, for the purpose of clarity,detailed descriptions of known devices, circuits, tools, techniques, andmethods are omitted so as not to obscure the description of the presentsystem. It should be expressly understood that the drawings are includedfor illustrative purposes and do not represent the entire scope of thepresent system. In the accompanying drawings, like reference numbers indifferent drawings may designate similar elements. The term and/or andformatives thereof should be understood to mean that only one or more ofthe recited elements may need to be suitably present (e.g., only onerecited element is present, two of the recited elements may be present,etc., up to all of the recited elements may be present) in a system inaccordance with the claims recitation and in accordance with one or moreembodiments of the present system.

FIG. 1A shows a side view of a portion of a fluid-sealed connector (FSC)100 of an implantable medical device (IMD) such as an implantablecardiac probe, phrenic nerve lead, deep brain stimulator, cochlearimplant, vagal nerve stimulator, etc., that may be utilized togetherwith a magnetic resonance (MR) imaging system (MRI) in accordance withembodiments of the present system. The FSC 100 may include segment leadsillustratively shown as first and second conductive segment lead wires(SLWs) 114 and 116, respectively and an outer cover 108 including aninner wall 102. The inner wall 102 may form a cavity 109 in which theSLWs 114, 116 are located at opposed end walls 118. The end walls 118may operate to seal the cavity 109 with respect to the SLWs 114, 116and/or to otherwise secure a position of the SLW 114 with respect to theSLW 116. The dimensions of the outer cover may be sized as desiredthough generally, the outer cover has a small length and width tofacilitate implantation and/or to facilitate that a length of each ofthe SLWs satisfy other criteria as discussed further herein.

The term seal and formatives thereof as utilized herein is intended toindicate that a barrier is created (e.g., a fluidic barrier) by theouter cover (e.g., the outer cover 108) generally and betweencorresponding surfaces when present as discussed that resists escapingof for example a fluid through the barrier. In this way, in accordancewith embodiments of the present system, a conductive material such as aliquid contained within the cavity, such as the cavity 109, cannotescape through the barrier or otherwise escape out of the cavity andmatter such as fluids including liquid and gaseous fluids not containedtherein cannot otherwise enter the cavity. In general it is significantin accordance with embodiments of the present system that what iscontained within the cavity is significantly maintained in the cavityand material not contained in the cavity is substantially kept out. Inaccordance with embodiments of the present system, the outer cover, suchas the outer cover 108 may be formed to provide a seal that may beimpermeable, semi-permeable or permeable to given ions, given ionicsolutions and/or given gases while being impermeable to the conductivematerial such as the given ionic solution contained therein.

In accordance with further embodiments of the present system, the outercover described herein and corresponding FSC may be formed to notprovide a seal (i.e., in these embodiments, the FSC is not “sealed”) andthereby may be semi-permeable or permeable to given ions, given ionicsolutions and/or given gases including to the conductive material suchas the given ionic solution contained therein. For example, the outercover may be purposefully formed with a “leaky seal” thereby enablingions, ionic solutions and/or gases including the conductive materialinitially placed within the cavity, to pass in and out of the outercover through the leaky seal. In other embodiments, the outer cover maybe formed having pores and/or may be provided with holes after formationthat renders the outer cover semi-permeable or permeable to ions, ionicsolutions and/or gases including the conductive material initiallyplaced within the cavity. In an IMD wherein the environment of theimplant and an FSC that is not sealed typically includes electricallyconductive biological gases and/or biological liquids, conductivitybetween conductors within the cavity as described herein is maintainedin these embodiments even though the outer cover is not sealed. Forexample, in an embodiment wherein the outer cover is not sealed,conductivity between conductors within the cavity as described herein ismaintained by one or more of the conductive material initially placedwithin the cavity, the biological gas(es) and/or the biologicalliquid(s) being within the cavity in contact with the conductors.

In accordance with embodiments of the present system, a first end 110 ofthe outer cover 108 may be sealed (e.g., glued, formed, ultrasoundwelding, laser welding, RF welding, glass seal, metal forming, elastomerlayer bonding, UV-cured adhesive seal, any combinations thereof, and/orother suitable technology on consideration of the materials utilizedthat provides a seal such as a hermetic seam, etc.) to the SLW 114 toseal the cavity 109 with regard to the first end 110 and the SLW 114. Inaddition to the seal, the first end 110 of the outer cover 108 may befurther structurally connected to the SLW 114 to secure a position ofthe SLW 114 in relation to the SLW 116. For example, one or more methodssuch as described above may be utilized to provide a seal while one ormore of the methods is utilized to provide a further structuralconnection with or without providing an additional seal. Similarly, asecond end 112 of the outer cover 108 may be sealed to the SLW 116 toprovide a barrier between the cavity 109 and the SLW 116. Further, thesecond end 112 of the outer cover 108 may provide a seal and may beadditionally structurally connected to the SLW 116 to secure theposition of the SLW 116 in relation to the SLW 114. Details within thecavity 109 are excluded from this view for the sake of clarity.

In accordance with embodiments of the present system, the opposed endwalls 118 may be sealed about the first and second SLWs 114 and 116,respectively, at seals 119 which may be drawn away from the cavity 109of the outer cover 108. However, it is also envisioned that the seals119 may fit flush with exterior portions of the opposed end walls 118 inaccordance with further embodiments of the present system such as shownin FIG. 1C. FIG. 1C shows a side view of a portion of an FSC of animplantable medical device in accordance with embodiments of the presentsystem wherein seals of an outer cover 108C fit flush with the opposedend walls. The outer cover 108 c has a length L_(C) and a width W_(C)that may vary in scale. In accordance with embodiments of the presentsystem, the length L_(C) and the width W_(C) for example may each bewithin a range of 1 to 0.1 inches (e.g., 0.113 inches), within a rangeof 0.5 to 0.1 inches, within a range of 0.3 to 0.1 inches as desired.The length L_(C) may have different dimensions from the width W_(C) andmay vary within a different range and larger and smaller dimensions areconceived suitable for an implantable device. It should be appreciatedthat the dimensions for all of the embodiments described herein may alsovary as in the embodiment shown in FIG. 1C.

The first and second SLWs 114 and 116, respectively, may be coated toenhance sealing of the cavity. In accordance with embodiments of thepresent system, the cavity 109 may be hermetically sealed to containfluid within the cavity as discussed further herein. The outer cover 108may be formed from any suitable material or combination of materials(e.g., a non-conductive material) such as a ceramic, a polymer, etc., toseal the cavity and may further act to hold the first and second SLWs114, and 116, respectively, in place relative to each other. Thematerial of the outer cover should be selected with consideration to theenvironment in which the outer cover is placed during use. For example,in an embodiment wherein the outer cover is intended for implantation,the outer cover material should be selected to be suitable forimplantation as appreciated such as a biocompatible material. While theouter cover is illustratively shown having differing forms in thevarious views provided in the figures, other shapes and forms may besuitably applied as long as the provided outer cover seals an inside ofthe cavity from an outside of the cavity. For example, FIG. 1B shows aside view of a portion of an FSC of an implantable medical device inaccordance with embodiments of the present system wherein an outer coveris formed by two end caps 108 _(B1) and an outer sleeve 108 _(B2). Asshown by dashed lines, the two end caps 108 _(B1) extend into the outersleeve 108 _(B2) for a distance as desired to enable the outer cover toprovide a seal as previously discussed. The two end caps 108 _(B1)and/or corresponding extensions may be sealed to the outer sleeve 108_(B2) using any suitable sealing technology such as described herein.Further, each end of the outer sleeve 108 _(B2) may be crimped, tied(e.g., utilizing a tie-wrap), etc., to a corresponding end cap 108 _(B1)to facilitate sealing. As readily appreciated, the outer cover andcorresponding SLWs may be sized (e.g., the length L_(B) and the widthW_(B)) and for example sealed as previously discussed.

FIG. 1D shows a side view of a portion of an FSC of an implantablemedical device in accordance with embodiments of the present systemwherein an outer cover is formed by two end caps 108 _(D1) and an innersleeve 108 _(D2). As shown by dashed lines, the inner sleeve 108 _(D2)extends into the two end caps 108 _(D1) for a distance as desired toenable the outer cover to provide a seal as previously discussed. Theinner sleeve 108 _(D2) and/or corresponding extensions may be sealed tothe two end caps 108 _(D1) using any suitable sealing technology such asdescribed herein. Further, each of the two end caps 108 _(D1) may becrimped, tied (e.g., utilizing a tie-wrap), etc., to a corresponding endof the inner sleeve 108 _(D2) to facilitate sealing. As readilyappreciated, the outer cover and corresponding SLWs may be sized (e.g.,the length LD and the width W_(D)) and for example sealed as previouslydiscussed. FIG. 2 shows an end view of a portion of the FSC 100 of FIG.1A in accordance with embodiments of the present system. The inner wall102 may be situated about the cavity 109 formed by the outer cover 108and may be coupled to an SLW such as the SLW 116. The outer cover 108including the opposed end wall 118 and the seal 119 may seal the cavity109 as discussed herein. The outer cover 108 may further provideelectrical isolation and may be formed having a given thickness forexample suitable for a desired electrical isolation. An end view of theother end may be similar and is not shown for the sake of brevity.

FIG. 3 shows a cutaway view of a portion of the FSC 100 taken alonglines 3-3 of FIG. 2 in accordance with embodiments of the presentsystem. The SLW 114 is shown electrically coupled to a conductorillustratively shown as a first 130 cylinder which is conductive. Thefirst cylinder 130 may include a cylindrical wall portion 148 defining acavity 152 having an open end 138. The cylindrical wall portion 148 iselectrically coupled to an adjacent SLW such as the SLW 114 using anysuitable method via an end wall 134. A second conductor illustrativelyshown as a second cylinder 132 may be shaped similarly to the firstcylinder 130 but may be sized such that at least a portion of the secondcylinder 132 may fit within the cavity 152 of the first cylinder 130with a desired spacing between portions of the first and secondcylinders 130, 132, respectively. In accordance with embodiments of thepresent system, the first and second conductors (e.g., the cylinders130, 132) do not physically contact each other. Accordingly, the secondcylinder 132 may include a cylindrical wall portion 150 spaced apartfrom the cylindrical wall portion 148 of the first cylinder 130. Inaccordance with embodiments of the present system, the second cylinder132 may be hollow defining a cavity 146 having an open end 140. Inaccordance with further embodiments of the present system, the secondcylinder 132 may be a solid cylinder such that there is no cavity withinthe second cylinder 132. The cylindrical wall portion 150 iselectrically coupled to an adjacent SLW such as the SLW 116 using anysuitable method via an end wall 136. In accordance with embodiments ofthe present system that may be suitably employed, the SLW and conductormay be formed together with the corresponding conductor as a singlecontinuous conductor such that no separate coupling therebetween isrequired.

A disc 144 may optionally be situated within the cavity 152 of the firstcylinder 130 and may isolate the first and second cylinders 130 and 132,respectively, from each other as may be desired. Accordingly, the disc144 may have a similar cross section as a cross section defined by thecylindrical wall 148 of the first cylinder 130. The disc 144 may beformed from any suitable material such as a ceramic, a polymer, etc.,which may act as a dielectric isolator. Although the second cylinder 132is illustratively shown spaced apart from the disc 144, in accordancewith further embodiments of the present system, the second cylinder 132may rest against the disc 144. In these embodiments, the disc 144 mayprovide positional stability to the second cylinder 132 with respect tothe spacing from the first cylinder 130.

In accordance with embodiments of the present system, a conductivematerial such as a gel, a fluid, etc., illustratively discussed as afluid 160 which may be formed as a buffer, an ionic solution, aconductive fluid, etc., may be situated within the cavity 109 and thecavity 146 when present (i.e., in an embodiment wherein the secondcylinder 132 is hollow). Thus, the first and second cylinders 130, 132,respectively, electrically insulated from each other due to the twophysically separated metallic conductors (e.g., the first and secondcylinders 130 and 132) are electrically coupled via the fluid 160. Inaccordance with embodiments of the present system, the fluid 160 mayfurther attenuate undesirable signals such as signals that otherwise maybe induced by radiofrequency (RF) signals into the SLWs 114, 116 fromexternal sources such as from an RF signal emitted from an MR system.

In the embodiment shown in FIG. 3, the cylinder 130 is illustrativelyshown directly adjacent to the inner wall 102 of the outer cover 108which in the embodiment shown, may provide positional stability to thefirst cylinder 130. In accordance with further embodiments of thepresent system, one or more portions of the first cylinder 130 (e.g.,one or more of the cylindrical wall portion 148 and the end wall 134)may be spaced apart from the outer cover 108 with the spacing filled bythe conductive material (e.g., the fluid 160). Further, in theembodiment shown in FIG. 3, the cylinder 132 is illustratively showndirectly adjacent to the inner wall 102 of the outer cover 108 which inthe embodiment shown, may provide positional stability to the secondcylinder 132. In accordance with further embodiments of the presentsystem, one or more portions of the second cylinder 132 (e.g., the endwall 134) may be spaced apart from the outer cover 108 with the spacingfilled by the conductive material (e.g., the fluid 160).

It is envisioned that embodiments of the present system may provide aconnector which may include metallic conductors (e.g., first and secondcylinders) which may each be individually attached to an adjacent SLW(e.g., metallic wire) external to the corresponding metallic conductor.The metallic conductors may be coupled to each other such as via a fluidsuch as an ionic fluid that may be situated between the metallicconductors. Accordingly, an electrical coupling between the metallicconductors inside the connector (e.g., the FSC 100) may be obtained viathe fluid. A shape and dimension of the metallic conductors and astrength (e.g., conductivity) and chemical composition of the fluid(e.g., the ionic solution) may be adjusted as required.

For example in a case wherein the conductive material is a conductiveliquid, a saline solution with 0.9% (or 9 gram/1 liter) of sodiumchloride (NaCl electrolyte) dissolved in water may be utilized withinthe cavity in accordance with embodiments of the present system. Theconductivity of this saline fluid is approximately 17.0 mS/cm (millisiemens per cm). Other appropriate concentrations and/or solutions thatconduct ionically may also be used. In accordance with embodiments ofthe present system, the conductivity of a conductive solution may beincreased which may enable smaller conductors and outside cover ordecreased as desired and still operate in accordance with embodiments ofthe present system. Further, a 3.0% NaCl solution (or 30 gram/1 literwater) having a conductivity of approximately 48.6 mS/cm, a 5.0% NaClsolution having a conductivity of approximately 81.0 mS/cm or a 0.5%NaCl solution having a conductivity of approximately 9.48 mS/cm may beutilized in accordance with embodiments of the present system thoughother concentrations and/or ionic solutions (e.g., potassium chloridesolution, KCl) may be suitably applied.

For example, organic acids or other fluids with a conductivity lowerthan metals may be suitably utilized in accordance with embodiments ofthe present system. As readily appreciated, the impedance of the FSCwill depend on the conductivity of the conductive material (e.g., theconcentration of an ionic solution), the surface area of the conductorswithin the cavity and the separation between the conductors. Theimpedance of the FSC may be adjusted as desired by changing any one ormore of these variables. As desired, a different ionic solution forexample such as an acid may be used as these have much higherconductivity than the saline solution. However, for an implantabledevice, the biocompatibility of the conductive material such as salinemay be a consideration for selection of the conductive material as wellas the suitability of the conductive material to the conductors and theouter cover.

In accordance with embodiments of the present system, the conductorswithin the cavity may be formed from a metal such as stainless steel,platinum, titanium, gold, silver, or other conductive materials such asgraphite or graphene carbon nanotubes. In any event, the material of theconductors is selected to have a greater conductivity than theconductive fluid. In addition, in accordance with embodiments of thepresent system, the conductors may have a porous surface, may haveincreased surface roughness and/or may have a corrugated shape toimprove conductivity between the conductors resultant with the fluid. Inaccordance with embodiments of the present system, in place of the firstand second cylinders, the contacts may have other configurations such asdual wire electrodes in parallel (i.e. radially) or axially (i.e.,butt-to-butt) comprised of two conductors in the same axis though notmaking physical contact, dual helical (coil shape) conductors, dualspiral conductors, dual disk conductors, dual plate conductors, etc.

For example, FIG. 12A shows a cutaway side view of a portion of an FSCin accordance with embodiments of the present system where contacts1230A, 1232A are similarly cylindrically shaped (e.g., dual diskconductors) and include an outer cover 1208A containing a conductivefluid 1260A. FIG. 12B shows a cutaway side view of a portion of an FSCin accordance with embodiments of the present system where contacts1230B, 1232B are similarly rectangular (e.g., square dual plateconductors) shaped with rounded corners though other similar embodimentsmay have right angles or substantially right angled corners and includean outer cover 1208B containing a conductive fluid 1260B. FIG. 12C showsa cutaway side view of a portion of an FSC in accordance withembodiments of the present system where contacts 1230C, 1232C aresimilarly elongated conductors (e.g., wire conductors) extending towardseach other (e.g., dual wire electrodes in parallel axially,butt-to-butt) and include an outer cover 1208C similar to the outercover 108 shown in FIGS. 1A, 3 containing a conductive fluid 1260C. Oneor more of the contacts 1230C, 1232C may be provided as continuousextensions of corresponding SLWs or may be separately coupled thereto.FIG. 12D shows a cutaway side view of a portion of an FSC in accordancewith embodiments of the present system where contacts 1230D, 1232D aresimilarly elongated conductors (e.g., dual wire conductors in parallelarranged radially) extending towards and past each other withouttouching and include an outer cover 1208D similar to the outer cover 108shown in FIGS. 1A, 3 containing a conductive fluid 1260D. One or more ofthe contacts 1230D, 1232D may be provided as continuous extensions ofcorresponding SLWs or may be separately coupled thereto. FIG. 12E showsa cutaway side view of a portion of an FSC in accordance withembodiments of the present system wherein contacts are similarlycomplementary shaped ridged contacts 1230E, 1232E and include an outercover 1208E containing a conductive fluid 1260E. FIG. 12F shows acutaway side view of a portion of an FSC in accordance with embodimentsof the present system where contacts 1230F, 1232F are similarlyelongated conductors (e.g., wire conductors) extending towards and pasteach other intertwined (e.g., dual helical coil shape, conductors, dualspiral conductors, etc.) without touching and include an outer cover1208F containing a conductive fluid 1260F. One or more of the contacts1230F, 1232F may be provided as continuous extensions of correspondingSLWs or may be separately coupled thereto.

In accordance with embodiments of the present system, the surface of oneor more of the conductors of these and/or other embodiments may beporous, may have holes (e.g., arranged randomly along one or more of theconductors or arranged in a pattern), may have ridges, or may have acorrugated surface shape (alternate ridges and grooves) to increasesurface contact with the fluid and thereby improve the conductivitybetween the conductors. As appreciated, better conductivity enablesreducing a size of the FSC while still operating (e.g., conductingphysiological pulses while reducing incidence of induced standing waves)in accordance with embodiments of the present system. In accordance withembodiments of the present system, the conductors may be of the samematerial, dissimilar materials, and/or may be coated with differentmaterials from the underlying portion to provide desired characteristics(e.g., to increase conductivity of the conductors and/or to providesuitability to the conductive material contained within the cavity ofthe outer cover).

Accordingly, embodiments of the present system may provide a lead wire(e.g., the FSC 100) suitable for an IMD which may be used in or in thevicinity of radiofrequency (RF) emitters such as an MR system includinga magnetic resonance imaging (MRI) system. Embodiments of the presentsystem may reduce or otherwise entirely prevent undesirable interactionwith RF emitters which may, for example, contribute to radiofrequency(RF) induced heating of metallic lead wires which may cause thermalinjury to tissue near to the lead such as at an end of the lead (e.g. alead tip) and/or an implanted probe.

For example, RF induced heating of a conventional lead (CL) may occurwhen the CL acts as an antenna capable of receiving and supporting thefrequency of an MR system's RF field. RF induced heating of the leadwire is most pronounced when a length of the lead wire (e.g., CL) inimplanted tissue (i.e., dielectric medium) is close to a resonancelength (e.g., one-half wavelength) of the RF emissions of the MR system.For example, an MR system that provides an RF field of 1.5 Teslaoperates at approximately 64 MHz and thereby provides an in airequivalent one-half wavelength of approximately 2.3 m. An MR system thatprovides an RF field of 3.0 Tesla operates at approximately 128 MHz andthereby provides an in air equivalent one-half wavelength ofapproximately 1.2 m. An MR system that provides an RF field of 7.0 Teslaoperates at approximately 300 MHz and thereby provides an in-airequivalent one-half wavelength of approximately 0.5 m.

However, in accordance with embodiments of the present system, it isfound that within the body, due to the relative dielectric constant, theone-half wavelength may be reduced by approximately a factor of 90 i.e.,to 26 cm for a 1.5 Tesla system, 14 cm for a 3.0 Tesla system and 6 cmfor a 7.0 Tesla system.

In accordance with embodiments of the present system, lead segments(e.g., SLW such as each of SLW 114, 116) including a length of thecorresponding conductor within the cavity (e.g., cylinders 130, 132)shorter than the one-half wavelength length of the RF signal of an MRIsystem may be employed (e.g., less than half of the wavelength length orless than 6 cm for a 7T MR system) and may reduce or entirely preventthe formation of standing waves induced by the RF emissions of the MRsystem.

Embodiments of the present system may provide a lead suitable (e.g., FSC100) for use in an MR environment in which a lead having a plurality ofsegments (e.g., lead segments such as SLWs 114 and 116) each of whichmay be formed from a metallic material as described and which may have alength of less than one-half wavelength of an emitted signal from an RFcoil of an MR system employed (e.g., intended to be used for theclinical investigation). The plurality of lead segments are seriallycoupled together in such a way that the subsequent full length lead wire(e.g., from an outside end of SLW 114 to an outside end of SLW 116) isable to conduct physiological stimulating or recording signals so as toreduce or entirely prevent (e.g., by fully or partially attenuating) thetransmission of the RF signals thus greatly reducing (e.g., reducing bymore than 90%) or totally eliminating the formation of standing wavesgenerated as a result of the RF emissions and minimizing an RF heatingeffect upon an object in close proximity to the lead.

Accordingly, embodiments of the present system may provide an implanteddevice compatible for use in conjunction with MR systems as well ascomponents for the implanted device (such as a lead wire or lead wiresegment connector) and associated methods of construction and use.Embodiments of the present system may overcome potential issuesassociated with transmission by lead wires of the implanted device suchas induced signal components associated with the radio frequency (RF)signal of the MR system which may cause heating of metallic lead wiresand may cause thermal injury to adjacent tissue.

In accordance with embodiments of the present invention, a method isprovided for constructing an implanted medical device that may be usedin conjunction with a MR system. For example, the implanted medicaldevice may be a cardiac pacemaker, defibrillator, nerve stimulator,brain stimulator, or cochlear implant. The implanted medical device mayinclude at least one component that may be implanted in a patient andmay include external components. The method may include acts ofproviding a lead wire for the implanted medical device having a totallead wire length greater than one-half of the MRI system's RF signalwavelength length and/or adapting the lead wire to inhibit transmissionof the MR system's RF signal as described. In this regard, the one-halfwavelength length dimension may be approximately six centimeters for a7.0 Tesla MR system, but may be longer or shorter for other MR systems.

Any adaptation to the lead wire that inhibits transmission therein ofthe MR system's RF signal may be utilized in accordance with presentinvention. In accordance with embodiments of the present system the leadwire may be a metallic lead wire and the act of adapting may include 1)segmenting the lead wire into segments (e.g., each of SLW 114, 116) eachhaving segment lengths less than one-half wavelength length of MRsystem's RF signal, and 2) connecting the segments in a manner thatinhibits transmission of the RF signal between the connected segmentssuch as described herein. For example, the coupling between the first130 cylinder and the second cylinder 132 via the conductive materialsuch as the fluid 160 may operate interposed between the segments toselectively transmit a signal of the implanted medical device andinhibit an induced transmission of the MR system's RF signal. Where thesignal of the implanted medical device has a frequency different thanthe RF signal, the lead wire including the conductors (e.g., the FSC100, 400, 800, etc.) may thus function to pass the medical device signaland inhibit transmission of the RF signal on a frequency dependentbasis. In this way in accordance with embodiments of the present system,the induced RF component may be selectively removed.

It will be appreciated that, in the context of an implantable device, itis desirable to achieve this RF inhibiting function in a compact design.Accordingly, RF filters deployed in other contexts may not be suitablefor use in this context. In the embodiments of the present systemdescribed herein, a conductive material such as a buffer material (e.g.,the solution 160) is provided at least between the first and secondconductors (e.g., the first and second cylinders) of the first andsecond segments (e.g., each of the SLWs 114, 116) of the lead wire. Thebuffer material may be a conductive fluid having appropriate signalproperties with respect to the configuration of the connector (e.g., thespacing between the leads). For example, the buffer material may be anionic solution.

In accordance with another aspect of the present system, an implantedmedical device may be provided for use in conjunction with an MR system.The implanted medical device may include a signal generator providing astimulus signal for use by the implanted medical device, a stimulus unit(e.g., an interface probe) for receiving the stimulus signal andapplying a stimulus to a patient, and one or more lead wires (e.g., theFSC 100, 400, 800, etc.) for use in transmitting the stimulus signalbetween the signal generator and the stimulus unit. Depending on thenature of the implanted medical device, the signal generator may be partof the implanted unit or may be part of an external unit. The lead wiremay have a total lead wire length greater than one-half wavelengthlength of an MR system's radio frequency signal and may be adapted toinhibit transmission therein of the MR system's RF signal. The lead wiremay be constructed in accordance with embodiments of the present system.

In accordance with a still further aspect of the present system, anaccessory component of an implanted medical device for use in connectionwith a MR system may be provided. The accessory component may include alead wire for the implanted medical device having a total lead wirelength greater than one-half wavelength length of the MR system's RFsignal as described herein which may inhibit an induced transmissiontherein of the MR system's RF signal. The lead wire may be constructedin segments (e.g., each of the FSWs 114, 116) each having a length lessthan one-half wavelength length of the MR system's RF signal with thecavity and conductive material interposed between segments as describedherein.

In accordance with a still further aspect of the present system, a leadline (e.g., FSC) of an implanted medical device is provided for use inconjunction with a MR system. The lead wire may have a total lead wirelength greater than one-half wavelength length of the MRI system's RFsignal and may be composed of segments having segment lengths less thanone-half of the noted wavelength length. The connector may include afirst conductor associated with a first connected segment of the leadwire (e.g., a conductor associated with the SLW 114), a second conductorassociated with a second connected segment of the lead wire (e.g., aconductor associated with the SLW 116), and a gap situated between thefirst and second conductors with an appropriate buffering material, suchas an ionic fluid, disposed in the gap that may selectively transmit asignal of the implanted medical device and may inhibit an inducedtransmission of the MR system's RF signal.

FIG. 4 shows a cutaway exploded side view of a portion of an FSC 400 inaccordance with embodiments of the present system. The FSC 400 may besimilar to the FSC 100 and may include first and second conductorsillustratively shown as first and second cylinders 430, 432,respectively, a disc 444, and first and second SLWs 414, 416,respectively. The first cylinder 430 may include a cylindrical wall 448defining a cavity 452 and having an end wall 434. Similarly, inaccordance with embodiments of the present system, the second cylinder432 may include a cylindrical wall 450 defining a cavity 446 and havingan end wall 436 or the second cylinder may be solid as described herein.

The first SLW 414 may be coupled to (electrically and physically) an endwall 434 of the first cylinder 430 via a conductive layer 415 and thesecond SLW 416 may be coupled to (electrically and physically) the endwall 436 of the second cylinder 432 via a conductive layer 425. Thefirst and second cylinders 430, 432, respectively, may be at leastpartially formed from a conductive material so as to be electricallycoupled to the respectively attached SLWs 414, 416. The first and secondSLWs 414, 416 may include an insulating layer 417 which may providephysical and/or electrical isolation to the respective conductive layer415, 425 (i.e., by surrounding the respective conductive layer as shown)of the respective first and second SLW 414, 416.

The disc 444 may be situated between an end wall 451 of the cylindricalwall 450 of the second cylinder 432 and an interior portion 435 of theend wall 434 of the first cylinder 430 and may be formed from one ormore insulating materials so as to insulate adjacent portions of thefirst and second cylinders 430, 432, respectively, from each other. Athickness TD of the disc 444 may be varied to provide a desired level ofisolation and/or attenuation of desired signals. At least a portion ofthe cavity 452 of the first cylinder 430 and a portion of the cavity 446of the second cylinder 432, when present, may be filled with aconductive material, (e.g., a fluid) such as an ionic fluid formed inaccordance with embodiments of the present system.

FIG. 5 shows a cutaway view of a portion of the first cylinder 430 ofthe FSC 400 taken along lines 5-5 of FIG. 4 in accordance withembodiments of the present system. The end wall 434 is coupled to thecylindrical wall 448 and includes the interior portion 435 which may atleast partially seal an end of the cavity 452.

FIG. 6 shows a cutaway view of a portion of the second cylinder 432 ofthe FSC 400 taken along lines 6-6 of FIG. 4 in accordance withembodiments of the present system. The end wall 436 is coupled to thecylindrical wall 450 and includes the interior portion 437 (e.g., inembodiments wherein the second cylinder is hollow) which may at leastpartially seal an end of the cavity 446.

The first and second cylinders 430, 432, respectively, may have similarcross-sectional shapes (e.g., round in the present embodiments) but maybe sized differently such that the second cylinder 432 may fit within atleast a portion of the cavity 452 of the first cylinder 430. Withoutlimitation, although a round cross-sectional shape is shown for thefirst and second cylinders 430, 432, other shapes including crosssectional shapes such as ellipsoid, polygonal, etc., are also envisionedas may be desired.

FIG. 7 shows an end view of a portion of the disc 444 of FIG. 4 inaccordance with embodiments of the present system. The disc 444 may havea cross section which may be similar to the cross sectional shape of thefirst cylinder 430. However, the disc 444 may be sized (e.g., indiameter) such that it is smaller than a diameter of an interior surfaceof the cylindrical wall 448 so as to fit within the cavity 452 of thefirst cylinder 430.

FIG. 8 shows a cutaway side view of a portion of an FSC 800 inaccordance with embodiments of the present system. The FSC 800 may besimilar to the FSC 100 and may include an outer cover 808 which maydefine at least part of a cavity 809 in which a a conductive material(e.g., an ionic fluid solution such as electrolyte saline or othersuitable ionic solution or fluid) 860 may be located. First and secondSLWs 814, 816, respectively, may be coupled to adjacent portions offirst and second cylinders 830, 832 such as to respective end walls ofthe first and second cylinders 830, 832 via respective conductive layers815, 825. The first and second SLWs 814, 816, respectively, may includea suitable insulator such as insulation 817 which may electricallyinsulate a corresponding one of respective conductive layers 815, 825 ofthe first and second SLWs 814, 816, respectively.

The outer cover 808 may be formed from any suitable material such as apolymer, silicon, silicon composite (e.g., Silastic™) which may form aseal around the cavity 809 to contain the conductive material. However,other materials for the outer cover 808 such as ceramic, etc., are alsoenvisioned. In accordance with embodiments of the present system, theouter cover 808 may be formed by one or more layers of material, such astwo or more layers of material (e.g., illustratively shown as two layersof material) one or more of which (e.g., an inner layer) may seal thecavity 809. While the outer cover 808 is illustratively shown as beingovoid-shaped, other shapes may also be suitably employed in accordancewith embodiments of the present system.

In accordance with embodiments of the present system, the fluid 860 maysituated about the contacts of the first and second cylinders 830, 832including within one or more cavities thereof. In this way, transmissionof electrical impulses between the first cylinder 830 and the secondcylinder 832 may occur via the fluid 860 as further described herein. Adisc 844 may act as a bumper to physically and/or electrically separatethe first and second cylinders 830, 832, respectively, from each other.

FIG. 9 shows a portion of a system 1200 in accordance with embodimentsof the present system. For example, a portion of the present system 1200may include one or more of an FSC 1202, an interface probe 1240, aprocessor 1210 (e.g., a controller), a memory 1220, sensors 1230, asignal generator 1260, and a network interface 1250. The probe 1240(such as an implanted interface probe or the like) may be coupled todesired tissue such as cardiac tissue, nerves tissue, etc.). Theprocessor 1210 may be operationally coupled to one or more of the memory1220, the sensors 1230, the signal generator 1260, and the networkinterface 1250. One or more of the elements shown in FIG. 9 may beimplanted into a patient or more be external to the patient. Though thesignal generator 1260 is illustratively shown as separate from theprocessor 1210, it is readily appreciated that the signal generator 1260may be provided as a portion of the processor 1210.

The memory 1220 may be any type of device for storing application dataas well as other data related to the described operation. Theapplication data and other data are received by the processor 1210 forconfiguring (e.g., programming) the processor 1210 to perform operationacts in accordance with the present system. The processor 1210 soconfigured becomes a special purpose machine particularly suited forperforming in accordance with embodiments of the present system. Theprocessor 1210 may communicate with a user and/or an external devicesuch as an external telemetry device, so as to receive information fromthe user and/or external device via a network 1250. The network 1250 mayinclude any suitable network such as a proprietary network, aninput/output (I/O) port, a telephony network, a wide-area network (WAN),a local-area network (LAN), the Internet, an intranet, or (wirelesspersonal-area networks (WPANs), a wireless network such as Bluetooth,Zigbee, WiFi, etc.

The FSC 1202 may include one or more suitable FSCs operative inaccordance with embodiments of the present system and which may becoupled to each other in a serial and/or in a parallel arrangement. Inembodiments wherein more than one FSC is coupled together, considerationof coupled lead lengths is provided to avoid a coupled length that isreceptive to an induced standing wave from RF emissions of an MR systemas described herein.

The operation acts may include configuring the system 1200 by, forexample, configuring the processor 1210 to obtain information from anysuitable source such as from the sensors 1230, the interface 1240,and/or the memory 1220 and processing this information in accordancewith embodiments of the present system to obtain information desired bythe system such as feedback information. For example, the sensors 1230may include sensors which may detect vitals of a patient in which thesystem 1200 and/or portions thereof may be implanted. The processor 1210may then use this feedback information in accordance with one or moredesired algorithms to determine a desired stimulus signal (SS) andcontrol the signal generator 1260 to generate the desired SS which maybe included within a stimulus pulse train (SPT). The signal generator1260 may then provide the SPT to the FSC 1202 which may remove anyundesirable RF components which may be induced when subject to signalsfrom external systems such as an external MRI system which may generateRF signals. These RF signals may induce an undesired RF component withinthe SPT. The FSC 1202 may include one or more FSCs in accordance withembodiments of the present system and may receive the input SPT and maycondition the SPT to output a corresponding SPT (SPT′) which may beprovided to the interface probe 1240. The interface probe 1240 may thenoutput the SPT′. For example, the interface probe 1240 may output theconditioned SPT′ to a desired object such as to tissue of a patient inwhich the system 1200 or portions thereof may be implanted.

This process is illustrated with reference to FIG. 10 which shows ablock diagram illustrating a system 1300 operating in accordance withembodiments of the present system including an MRI system 1390 having anRF coil 1392 which may transmit RF signals. An SPT (e.g., as an inputSPT signal (SPT)) may be generated by a signal generator 1360 and may beprovided as an input to an FSC 1302. However, due to variouscircumstances, such as an external MRI system 1390, etc., the input SPTsignal SPT may include an undesirable RF component 1391 (e.g., generateddue to induced currents within the MRI system such as due to RF signalsfrom the RF coil 1392, etc.). The FSC 1302 operating in accordance withembodiments of the present system may block this RF signal at fluid(e.g., ionic solution, ionic fluid, etc.) 1360 which may act as anattenuating fluid. For example, the fluid 1360 within the FSC 1302 mayblock RF waves within the input SPT signal (SPT) and output acorresponding SPT signal (SPT′) as an output signal. Thus, the RFsignals may be fully or substantially inhibited or attenuated in theoutput SPT signal (SPT′). In accordance with embodiments of the presentsystem, the FSC 1302 may have a total lead wire length (lead length((L_(LEAD))) for example as indicated by a length between the arrows inthe figure) greater than one-half of the MRI system's RF signal.

Referring back to FIG. 9, the system 1200 may further provide a userinterface (UI) portion (UIP) which may include any suitable userinterface (UI) such as a keyboard, a mouse, a trackball and/or otherdevice, including touch-sensitive displays, which may be stand alone orbe a part of a system, such as part of a personal computer, a notebookcomputer, a netbook, a tablet, a smart phone, a personal digitalassistant (PDA), a mobile phone, and/or other device for communicatingwith the processor 1210 via any operable link. The UIP may be operablefor interacting with the processor 1210 including enabling interactionwithin a UI as described herein. Clearly the processor 1210, the memory1220, the sensors 1230, the interface probe 1240, the FSC 1202, thesignal generator 1260, and/or the UIP may all or partly be a portion ofa computer system or other device such as a client and/or server, animplanted medical device, and/or the like.

The methods of the present system are particularly suited to be carriedout by processor programmed by a computer software program, such programcontaining modules corresponding to one or more of the individual stepsor acts described and/or envisioned by the present system. The processor1210 may be operable for providing control signals and/or performingoperations in response to input signals from the UIP, the sensors 1230,as well as in response to other devices of a network and executinginstructions stored in the memory 1220. For example, the processor 1210may obtain feedback information from the sensors 1230 and may processthis information to determine how to drive the signal generator 1260 toemit a desired SPT. The sensors 1230 may include the interface probe1240 so as to provide a feedback signal to the controller 1210 such asthe coupling FSC 1202 or may utilize a different coupling similar to theFSC 1202 in a case wherein the sensors are implanted. In this way,induced RF signals may be blocked by the FSC 1202. In accordance withembodiments of the present system, the FSC 1202 may be bidirectionalthereby transmitting signals to and receiving signals from the interfaceprobe 1240.

The processor 1210 may include one or more of a microprocessor, anapplication-specific or general-use integrated circuit(s), a logicdevice, etc. Further, the processor 1210 may be a dedicated processorfor performing in accordance with the present system or may be ageneral-purpose processor wherein only one of many functions operatesfor performing in accordance with the present system. The processor 1210may operate utilizing a program portion, multiple program segments, ormay be a hardware device utilizing a dedicated or multi-purposeintegrated circuit. Further variations of the present system wouldreadily occur to a person of ordinary skill in the art and areencompassed by the following claims.

FIG. 11A shows a block diagram of a portion of a lead 1100A having aplurality of FSCs 1102 (e.g., nodes) coupled together in series inaccordance with embodiments of the present system. FIG. 11B shows ablock diagram of a portion of an IMD 1100B including the lead 1100Asituated between and coupling a signal generator 1160 and an interfaceprobe (IP) 1140 such as an implantable cardiac probe in accordance withembodiments of the present system. Referring to FIG. 11A, SLWs 1116 maybe coupled to corresponding FSCs 1102. The lead 1100A may include firstand second ends 1101 and 1103, respectively, defining a length(L_(LEAD)) along which at least one FSC 1102 may be located. The length(L_(LEAD)) is shown as a straight (or substantially straight) line forthe sake of clarity. However, without limitation it should be understoodthat this length may include other shapes such a curved line, etc. Forexample, it is envisioned that the lead 1100A may include a loop, acurve, a fold, etc. located along a length thereof. The IMD may be anysuitable IMD such as a cardiac pacemaker, a defibrillator, or otherneurostimulation devices (e.g., a phrenic nerve stimulators, deep brainstimulators, cochlear implants or vagal nerve stimulators). The IMD maybe implanted within a biological object such as patient, an animal, etc.

As illustratively shown, one or more FSCs 1102 may each be coupledtogether in series and/or in parallel as may be desired. At least one ofthe lead segments 1116 (such as a start lead segment 1116SL) may receivea signal from a signal generator and this signal (e.g., a drive signal)may be coupled to another of the lead segments 1116 (such as to an endlead segment 1116EL) via a fluid coupling of each FSC 1102 so as toattenuate signals induced by radiofrequency (RF) signals of an MR system(e.g., an MR imaging (MRI) or MR spectrography (MRS) systems) and passthe drive signal. Accordingly, during operation, the drive signal may befree of interference caused by, for example, MR signals such as MRinduced signals and/or RF interference generated by an MR system such asmay be encountered during an MRI scan. In accordance with embodiments ofthe present system, the lead 1100A may have a total lead wire length(e.g., from the start lead segment 1116SL to the end lead segment1116EL) greater than one-half wavelength length of the MRI system's RFsignal and may be composed of segments having segment lengths less thanone-half of a wavelength length. For example, a distance from the firstend 1101 to a distal end 1130A of a contact may be composed of a segmentlength less than one-half of a wavelength length. Similarly, a distancefrom a distal end 1132A of a contact to a distal end 1130B of a nextcontact may be composed of a segment length less than one-half of awavelength length. In this way a desired lead length (L_(LEAD)) may beformed while still providing any given segment length being less thanone-half of a wavelength length.

Finally, the above-discussion is intended to be merely illustrative ofthe present system and should not be construed as limiting the appendedclaims to any particular embodiment or group of embodiments. Thus, whilethe present system has been described with reference to exemplaryembodiments, it should also be appreciated that numerous modificationsand alternative embodiments may be devised by those having ordinaryskill in the art without departing from the broader and intended spiritand scope of the present system as set forth in the claims that follow.In addition, any section headings included herein are intended tofacilitate a review but are not intended to limit the scope of thepresent system. Accordingly, the specification and drawings are to beregarded in an illustrative manner and are not intended to limit thescope of the appended claims.

In interpreting the appended claims, it should be understood that:

a) the word “comprising” does not exclude the presence of other elementsor acts than those listed in a given claim;

b) the word “a” or “an” preceding an element does not exclude thepresence of a plurality of such elements;

c) any reference signs in the claims do not limit their scope;

d) several “means” may be represented by the same item or hardware orsoftware implemented structure or function;

e) any of the disclosed elements may be comprised of hardware portions(e.g., including discrete and integrated electronic circuitry), softwareportions (e.g., computer programming), and any combination thereof;

f) hardware portions may be comprised of one or both of analog anddigital portions;

g) any of the disclosed devices or portions thereof may be combinedtogether or separated into further portions unless specifically statedotherwise;

h) no specific sequence of acts or steps is intended to be requiredunless specifically indicated;

i) the term “plurality of” an element includes two or more of theclaimed element, and does not imply any particular range of number ofelements; that is, a plurality of elements may be as few as twoelements, and may include an immeasurable number of elements; and

j) the term and/or and formatives thereof should be understood to meanthat only one or more of the listed elements may need to be suitablypresent in the system in accordance with the claims recitation and inaccordance with one or more embodiments of the present system.

What is claimed:
 1. A lead wire assembly for an implantable medicaldevice (IMD), the assembly comprising: a lead having a plurality ofseparate conductive segments; a cover defining at least one cavitysituated about adjacent conductive segments of the plurality of separateconductive segments; and a fluid or gel located in the at least onecavity configured to couple a signal between the adjacent conductivesegments, wherein the cover is configured to be permeable to at leastone of a liquid, a molecule, an ion and a gas.
 2. The assembly of claim1, wherein the cover is impermeable to the coupling fluid or gel.
 3. Theassembly of claim 1, wherein the cover includes one of a leaky seal,pores or wholes that render the cover permeable to the at least one ofthe liquid, the molecule, the ion and the gas.
 4. The assembly of claim3, wherein the cover is configured to be implanted in a body portion ina presence of an electrically conductive biological gas and/orelectrically conductive biological liquid.
 5. The assembly of claim 4,wherein the cover is permeable to the electrically conductive biologicalgas and/or electrically conductive biological liquid.
 6. The assembly ofclaim 1, wherein the cover is secured to the adjacent conductivesegments to maintain a relative position between the adjacent conductivesegments.
 7. The assembly of claim 1, wherein the cover includes a sealto the adjacent conductive segments to maintain the cover impermeable tothe coupling fluid or gel.
 8. The assembly of claim 7, wherein the coveris secured to the adjacent conductive segments to maintain a relativeposition between the adjacent conductive segments.
 9. The assembly ofclaim 1, wherein the coupling fluid or gel electrically couples adjacentconductive segments to pass electrical signals between the adjacentconductive segments.
 10. The assembly of claim 1, wherein a liquid islocated in the cavity to couple the signal between the adjacentconductive segments.
 11. The assembly of claim 1, wherein a gas islocated in the cavity to couple the signal between the adjacentconductive segments.
 12. The assembly of claim 1, wherein a gel islocated in the cavity to couple the signal between the adjacentconductive segments.
 13. The assembly of claim 1, wherein the couplingfluid or gel further attenuates induced signals generated byradiofrequency (RF) signals of a magnetic resonance (MR) system.
 14. Theassembly of claim 1, wherein a total length of the lead defines a lengthwhich is greater than one-half wavelength length of radiofrequency (RF)signals generated by an MRI system.
 15. The assembly of claim 14,wherein a length of at least one of the plurality of conductive segmentsis less than one-half wavelength length of the radiofrequency (RF)signals generated by the MR system.
 16. The assembly of claim 1, whereinthe fluid is located in the at least one cavity to couple the signalbetween the adjacent conductive segments and the fluid comprises abuffer or an ionic solution.
 17. The assembly of claim 1, wherein thecover is one of a plurality of covers situated about correspondingadjacent conductive segments with each cover containing a fluid or gelto couple the signal between the corresponding adjacent conductivesegments.
 18. A lead wire assembly for an implantable medical device(IMD), the assembly comprising: a lead having a plurality of separateconductive segments; at least one cover defining at least one cavitysituated about corresponding adjacent conductive segments; and a fluidor gel located in the at least one cavity configured to couple a signalbetween the corresponding adjacent conductive segments, wherein the atleast one cover is sealed to the corresponding coupling fluid or gel.19. A method of forming a lead for conducting signals for an implantablemedical device (IMD), the method comprising acts of: forming a leadhaving a plurality of separate conductive segments; forming at least onecover defining at least one cavity in which corresponding adjacent endsof conductive segments are located; and positioning a signal conductivefluid or gel within the at least one cavity.